1. Field of the Invention
The present invention relates to a wireless communication system utilizing a frequency hopping method and a control method therefor.
2. Related Background Art
Wireless communication has recently shown remarkable progress and is being utilized in various fields. In particular, there are being proposed wireless systems for effecting the multimedia data communication.
In such wireless exchange systems, digital wireless communication methods are increasingly utilized. Among such digital wireless communication methods, spread spectrum (SS) communication is attracting particular attention. The spread spectrum communication is based on spreading the transmitted information over a wide band and is known to be splendid in the ability of eliminating disturbance and maintaining the privacy of communication. The spread spectrum communication is getting popularity through the world and a frequency band of 2.4 GHz is assigned for this purpose in various countries.
The spread spectrum communication can be roughly divided into a frequency hopping (FH) method and a direct spreading (DS) method. The former utilizes the wide frequency band by varying the modulating frequency within a predetermined time, while the latter effects spread modulation of the transmitted information with a pseudo noise code of a speed of ten to several hundred times.
In the spread spectrum communication of the frequency hopping method, plural communications can be achieved simultaneously by selecting the form of variation, or the hopping pattern (HP), of the modulating frequency. More specifically, multiplexed communications can be realized within a same time, by adopting different hopping patterns in the different communication terminals.
In such conventional system, therefore, a key terminal constituting a central control station manages the hopping patterns within the system, and any terminal executes communication with the hopping pattern obtained from such central control station.
However such conventional system has been associated with the following drawbacks.
During a communication between a first terminal and a second terminal, a third terminal, wishing to send an urgent message or data to the first or second terminal, is unable to do so by cutting into the communication because the hopping pattern (HP) used by the first and second terminals in the communication.
An object of the present invention is to enable, during a communication between a first terminal and a second terminal by the frequency hopping method, a third terminal to communicate with the first or second terminal.
Another object of the present invention is to enable a third terminal to cut into a communication between a first terminal and a second terminal, and, after a communication between the third terminal and the first or second terminal, to promptly restore the communication between the first and second terminals.
Still another object of the present invention is to enable a third terminal to cut into a communication between a first terminal and a second terminal, and, after a communication between the third terminal and the first or second terminal, to simply restore the communication between the first and second terminals without re-assignment of the hopping pattern.
Still another object of the present invention is, in case a third terminal cutting into a communication between a first terminal and a second terminal, to avoid collision of the data transmitted by the third terminal with the data communicated between the first and second terminals.